With the popularization of cell phones, portable computers and other small size electronic devices, there is a need to develop smaller and thinner semiconductor devices to be installed in them. In order to meet this need, BGA packages and CSP packages have been developed that have been put in practical application.
The BGA packages and CSP packages are semiconductor devices for surface mounting. Micro-balls for external connecting terminals are loaded onto one surface of the substrate of the package and are connected there. Several methods may be adopted to load the micro-balls. According to one method, a suction holding head is used. According to another method, a transfer mask is used.
According to the aforementioned method, as shown in FIG. 9(a), substrate (3) with semiconductor chip (1) encapsulated with resin (2) on it is loaded on a stage. Flux or solder paste is placed on terminal regions (4) (electrode lands) of substrate (3). Suction holding head (5) has suction and holding holes (7) for vacuum suction and holding micro-balls (6) (solder balls). While micro-balls (6) are gripped by suction and held, suction holding head (5) is driven to move towards substrate (3), and suction holding head (5) presses micro-balls (6) so that micro-balls (6) are loaded onto terminal regions (4), respectively. This method of loading micro-balls, for example, is disclosed in Patent Reference 1 and Patent Reference 2.
According to the latter method, as shown in FIG. 9(b), transfer mask (10) is arranged facing substrate (3). Through-holes (11) formed in the transfer mask (10) match the pattern of terminal regions (4) on substrate (3). As a result, micro-balls (6) fed onto transfer mask (10) fall through through-holes (11) and are loaded onto terminal regions (4). Then reflow is used to join micro-balls (6) and terminal regions (4) to each other with metal, forming the bump electrodes for external connection of the BGA package or CSP package. This method of loading micro-balls is described, for example, in Patent Reference 3.    Patent Reference 1: Japanese Kokai Patent Application No. 2001-332899    Patent Reference 2: Japanese Kokai Patent Application No. Hei 8[1996]-335771    Patent Reference 3: Japanese Kokai Patent Application No. 2004-327536
The micro-ball loading device using the transfer mask described above, has the following problems. As shown in FIG. 10(a), substrate (3) has resin (2) that is supported on backing plate (20), and transfer mask (10) is fixed at its end portion (10a) to a fixing table, not shown in the figure, so that transfer mask (10) and substrate (3) are arranged facing each other. Magnet (22) is arranged on the lower side of backing plate (20), and transfer mask (10) containing the metal mask is held onto backing plate (20) by the magnetic force of magnet (22), so that transfer mask (10) closely contacts substrate (3). In this state, the micro-balls (6) fall via through-holes (11) onto terminal regions (4).
After the loading of micro-balls (6), as shown in FIG. 10(b), backing plate (20) and magnet (22) are lowered, so that substrate (3) is released from transfer mask (10). In this case, the magnetic force of magnet (22) bends the central portion (10b) of transfer mask 10 more than end portions (10a) to form a concave shape, and release of transfer mask (10) is delayed more at central portion. When transfer mask (10) is bent, the deviation in position of through-holes (111) of transfer mask (10) in the vertical direction causes the positions of micro-balls (6) loaded on the substrate to also deviate from through-holes (11), and this is undesirable.
As shown in FIG. 11(a), transfer mask (10) contains metal mask (30) and resin layer (32) formed on its lower layer. Through-holes (11) in metal mask (30) are formed with a diameter slightly larger than that of micro-balls (6), and openings (34) are formed in resin layer (32) larger than the diameter of through-holes (11). After micro-balls (6) are loaded onto terminal regions (4) of substrate (3), transfer mask (10) is bent when substrate (3) is released from transfer mask (10), as explained above, and the precision of through-holes (11) deteriorates, so that as shown in FIG. 11(b), micro-balls (6) contact the side surface of through-holes (11) and stick there, so that micro-balls (6) cannot fall reliably onto terminal regions (4). This is undesirable.
Deviation in the positions of micro-balls and poor loading cause deterioration and defects of the semiconductor device. As a result, the yield falls and the manufacturing cost rises.
The purpose of the present invention is to solve the aforementioned problems of the prior art by providing a loading device and loading method for electroconductive balls characterized by the fact that the electroconductive balls can be loaded correctly and reliably on the terminal regions of the substrate.
Another purpose of the present invention is to provide a loading device and a loading method for electroconductive balls characterized by the fact that it can increase the yield of BGA packages or CSP packages or other surface mount semiconductor devices, and can lower their manufacturing costs.